Field of the Invention
The present invention relates to envelope tracking power amplifiers.
Description of the Prior Art
Envelope tracking power amplifier architectures are well-known, and an example of such is shown in FIG. 1.
In FIG. 1 an input signal is provided on line 22. The input signal is provided to a transmitter RF modulator block 20 before being delivered to the input of a power amplifier 18. The power amplifier 18 provides an RF amplified version of the input signal on line 24 as an RF output signal. The transmitter RF modulator block 20 modulates the input signal and also converts the input signal into an RF signal.
The input signal on line 22 is also provided as an input to an AM (amplitude modulation) block 12, which generates at its output an envelope signal representing the envelope of the input signal. The envelope signal is processed by an envelope tracking processing block 14 before providing a control input to an envelope tracked modulator 16. The envelope tracked modulator provides a supply voltage to the power amplifier 18 under the control of the envelope tracked signal provided by the envelope tracking processing block 14.
The envelope tracked processing block 14 may comprise a delay adjustment block 26, a pre-shaping gain and offset block 28, a post-shaping gain and offset block 32 and a digital-to-analogue converter block 34. As known in the art, the envelope tracked processing block 14 typically includes shaping block, denoted by reference numeral 30 in FIG. 1.
Thus, and with reference to FIG. 2, it is known to receive an input signal to be amplified in a step 40, and to modulate that received input signal to an RF input signal in a step 42. An envelope signal may be generated for an envelope tracking modulator in a step 44. An envelope tracked supply voltage may then be generated in a step 46. The envelope tracked supply voltage is provided to the power amplifier in a step 48 as the supply voltage. The power amplifier amplifies a modulated received input signal in dependence on the envelope tracked supply voltage to the power amplifier in a step 50, and generates an RF output signal at the output of the power amplifier in a step 52.
It is an aim of the present invention to provide an improvement to an envelope tracking architecture such as set out in FIG. 1, and in particular to provide an improved technique for shaping in the envelope path.